iMac making strange noise at boot (harddisk I think)

My (new) iMac makes a strange noise when I boot. It looks like the hard disk to me. As long as it makes the noise, it doesn't boot. After the noise is gone (sometimes in a minute, sometimes five). I have attached a file recorded with my iPhone to illustrate what I mean.
Is this normal or should I get back to Apple?

clicking in HDDs are baaaaad! all 3 of my western digitals started clicking before they went bust, if you have applecare, take it back. otherwise a new HDD is in order, and soon, if you dont want to lost your OS

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